1. Field of the Invention
The present invention relates generally to a photographing apparatus having an anti-vibration function, which incorporates a function to correct a vibration derived from a camera shake or the like of a photographer and, more particularly, to a photographing apparatus having an anti-vibration function, the apparatus being capable of exhibiting the anti-vibration function in a predetermined state even when the photographer intentionally performs a framing operation in which the photographing is effected by changing a photographing angle after being focused.
2. Related Background Art
In a recent photographing apparatus, e.g., a camera with an auto exposure (AE) mechanism, the autofocus (AF) mechanism and other respective elements are automated at a high level. A highly-functionalized element is a function to correct image blur derived from a camera shake, etc. which is caused when photography is conducted while holding the camera with hands. A variety of proposals are made.
That is, in this type of camera, there have hitherto been proposed a variety of vibration preventing devices each having a vibration correctable construction such that, for the purpose of correcting the image blur produced by camera shake, especially by tilting the camera, each speed sensor serving as a vibration detecting device detects the camera shake and the vibration, and a photographing lens system or a part of this photographing lens system serving as a principal optical system is shift-driven in a direction orthogonal to the optical axis in accordance with a result of the detection thereof.
Then, in the camera having such an anti-vibration function, the photographing lens system or some lens elements thereof are movably controlled as a vibration correction optical system, thereby obviating the image blur. Even when exposed at a shutter speed slower than that of ordinary photographing, it is possible to take a photo in a state where no image blur is caused.
In addition, this type of camera, a focus lock is used during preparation for photographing. And it may happen that the exposure operation is often performed after the shaking of the camera for changing the photographing angle. The detected vibration signal is influenced by the movement for changing the visual angle, resulting in a problem such that an anti-vibration accuracy can not be secured when performing the photographing exposure.
For obviating this problem, for example, Japanese Patent Application Laid-Open No. 5-142615 discloses a construction in which there is determined whether or not it is the time when photography is being conducted in relation to the visual angle changing operation. If this is determined as the visual angle changing operation, the vibration is corrected by applying a compensation to vibration detection signal.
According to the prior art disclosed in Japanese Patent Application Laid-Open No. 5-142615, however, it is difficult to determine whether it is the visual angle changing operation or not. Further, in the case of determining that it is the visual angle changing operation, complicated control has to be done. A burden is imposed on a CPU mounted in the camera, and, for effecting the processing at a high speed, a high-performance CPU has to be employed. There arises the problem in which this leads to an increase in costs for the camera as a whole.
Also, an angular speed sensor is the dominant vibration detecting sensor used for the anti-vibration function in the above-mentioned camera, etc. In the case of using such an angular speed sensor, however, a sensor output when the vibration reference value is normalized (i.e., where the vibration is considered to be zero or where the angular speed is zero) becomes unstable due to a drift or the like. There is produced such an inconvenience that this directly worsens the vibration correcting accuracy.
As a countermeasure against this, for instance, Japanese Patent Application Laid-Open No. 4-211230 discloses a construction in which an average value (shift average value) of the sensor outputs for a predetermined time is obtained and employed as the output representing the zero vibration reference value to correct the sensor output.
In the apparatus disclosed in Japanese Patent Application Laid-Open No. 4-211230, however, when the average value of the sensor outputs for the predetermined time is set as a zero vibration reference value of the sensor output, the the following problems arise.
That is, with respect to a still camera, a great majority of photographers often intentionally take a photograph such that a framing operation is carried out after being set in an in-focus state by performing the focusing operation irrespective of the autofocusing and manual focusing, and thereafter the exposure is carried out.
Then, in such a case, it follows that a biasing vibration, due to the framing before the exposure, is mixed as a bias component in the vibration detection output for the predetermined time in the apparatus disclosed in Japanese Patent Application Laid-Open No. 4-211230. If the shift average value of the vibration detection outputs is employed as the output representing the zero vibration reference value, the problem is that the vibration detection output can not be accurately corrected.
For this reason, in this type of vibration correctable camera, it is desired that the bias component be prevented from being mixed in the vibration detection output during the framing operation described above and the vibration correcting accuracy be increased during the exposure.
For responding to such demands, the present applicant examined, in detail, the states of the vibration detection output and the camera operation that is performed by the photographer during the framing operation and found out the following points.
That is, Japanese Patent Application Laid-Open No. 3-237411 gives a statement that it is better to work the vibration correcting function during the vibrating operation and discloses a method of temporarily inhibiting the work of the vibration correcting function by the manipulation of the photographer. This intends to avoid the situation such that the framing becomes hard to perform due to the restraint on the manipulation, such as panning by the photographer, by the vibration correcting operation.
Then, Japanese Patent Application Laid-Open No. 3-237411 states that when performing the framing operation after being focalized by the focusing, there may be operated a switch for temporarily inhibiting the work of the vibration correcting function.
According to the Publication described above, however, there is no statement about the measures for improving the accuracy of the vibration correcting function at the time of the exposure, and therefore some measures capable of satisfying such a point are required.
Further, Japanese Patent Application Laid-Open No. 3-237411 states that a switch is provided in a lens barrel unit, and the work of the vibration correcting function is temporarily stopped by the photographer's manipulation of this switch.
In the camera disclosed in the above Publication, however, when trying to temporarily stop the work of the vibration correcting function, a vibration correcting operation stop switch has to be operated each time. This results in a problem of being troublesome and causes a lack of the operability.
In addition, in the conventional camera having the anti-vibration function as disclosed in Japanese Patent Application Laid-Open No. 3-237411, it is known that an AF lock function and an AE lock function are functions frequently employed when performing the framing operation.
Then, according to the conventional camera, these AF and AE lock functions are made to work by manipulating respective dedicated lock operation switches or by a changeover operating switch incorporating both of these functions.
According to the conventional camera having the anti-vibration function described above, however, the photographer temporarily stops the work of the image framing correcting function to work the AF or AE lock function. For this purpose, the photographer has to simultaneously manipulate the lens-side vibration correction stop switch and the above-mentioned body-side lock function operating switch. Accordingly, the problem inherent in such a conventional camera is that the operability is diminished, and the usability is poor.